Search

Increased temperatures associated with urbanization (the "urban heat island" effect) have been shown to impact a wide range of traits across diverse taxa. At the same time, climatic conditions vary at fine spatial scales within habitats due to factors including shade from shrubs, trees, and built structures. Patches of shade may function as microclimate refugia that allow species to occur in habitats where high temperatures and/or exposure to ultraviolet radiation would otherwise be prohibitive. However, the importance of shaded microhabitats for interactions between species across urbanized landscapes remains poorly understood. Weedy plants and their foliar pathogens are a tractable system for studying how multiple scales of climatic variation influence infection prevalence. Powdery mildew pathogens are particularly well suited to this work, as these fungi can be visibly diagnosed on leaf surfaces. We studied the effects of shaded microclimates on rates of powdery mildew infection on Plantago host species in (1) "pandemic pivot" surveys in which undergraduate students recorded shade and infection status of thousands of plants along road verges in urban and suburban residential neighborhoods, (2) monthly surveys of plant populations in 22 parks along an urbanization gradient, and (3) a manipulative field experiment directly testing the effects of shade on the growth and transmission of powdery mildew. Together, our field survey results show strong positive effects of shade on mildew infection in wild Plantago populations across urban, suburban, and rural habitats. Our experiment suggests that this relationship is causal, where microclimate conditions associated with shade promote pathogen growth. Overall, infection prevalence increased with urbanization despite a negative association between urbanization and tree cover at the landscape scale. These findings highlight the importance of taking microclimate heterogeneity into account when establishing links between macroclimate or land use context and prevalence of disease. [ABSTRACT FROM AUTHOR]

Productivity in the Arctic is expected to increase as temperatures and the number of open water days rise. With this increased productivity, the coastal shelves of the Arctic Ocean may act as a sink for atmospheric carbon. However, this storage is dependent on a sufficient nitrogen (N) supply and current literature on biogeochemical rates of N uptake in this region is severely limited. Here, we report the spatial extent and rate at which the aquatic microbial community utilizes inorganic and organic N substrates in the Alaskan Arctic during late summer. Uptake rates (> 0.3 μm) were measured in 2016 and 2017 using isotopically labeled ammonium (NH4+), nitrate (NO3−), urea, and mixed algal amino acids. Rates of NH4+ regeneration were also measured to investigate the contribution of remineralized N to primary production. Primary production was estimated using isotopically labeled bicarbonate. We found that N species uptake varied by location. Although NH4+ was the form of N taken up at the greatest rate at most sites, we also found that uptake rates of urea could be greater than NO3− and that amino acid uptake was widespread. Supporting previous studies, NO3− uptake rates were correlated with primary production rates. Variability in nutrient reservoirs and sampling conditions in the Chukchi Sea between the 2 yr were responsible for some of the variances observed in estimated NH4+ recycling rates and primary production. Understanding which N sources support this late‐season primary production requires obtaining uptake rates for a diverse range of inorganic and organic N substrates. [ABSTRACT FROM AUTHOR]

The basal ganglia are intimately connected to the frontal cortex via five fronto-striatal circuits. While the role of the frontal cortex in cognition has been extensively studied, the contribution of the basal ganglia to cognition has remained less clear. In Parkinson's disease, posteroventral pallidotomy (PVP) involves surgical lesioning of the internal section of the globus pallidus (GPi, the final output pathway from the basal ganglia) to relieve the motor symptoms of the disorder. PVP in Parkinson's disease provides a unique opportunity to investigate the impact of disruption of striatal outflow to the frontal cortex on cognition. We assessed executive function and working memory after withdrawal of medication in 13 patients with Parkinson's disease before and 3 months after unilateral PVP compared to 12 age- and IQ-matched normals assessed twice with an interval of 3 months. The tests used were: Wisconsin Card Sorting (WCST), Self-Ordered Random Number Sequences, Missing Digit Test, Paced Visual Serial Addition Test (PVSAT), and Visual Conditional Associative Learning Test (VCALT). After PVP, the patients performed significantly better on the Self-Ordered Random Number Sequences and the WCST, an improvement that was also observed in the normals across the two assessment and is therefore likely to reflect practice effects. Relative to the normals, the patients showed significant differential change following PVP on the Missing Digit Test and PVSAT, on which they performed worse after compared to before surgery, while the controls performed better on the second assessment. For the patients, performance on the VCALT also indicated deterioration after PVP, but the changes approached significance. The side of PVP had no effect on the results. The pattern of change observed 3 months after PVP was maintained at 15-month follow-up. The results suggest that striatal outflow to the frontal cortex may be essential for those aspects of executive function that showed deterioration after PVP. [ABSTRACT FROM AUTHOR]

Here, we present the first study to investigate the seasonal importance of amino acid-nitrogen (N) to Arctic near shore microbial communities. We measured primary productivity and the uptake of ammonium, nitrate, urea, and amino acids in two size fractions (> 3 μm and approximately 0.7-3 μm), as well as ammonium regeneration and nitrification using 15N and 13C tracer approaches in the near-shore waters of the Chukchi Sea, during January, April, and August for two consecutive years. At discrete depths, nitrate comprised 46-78% of the total dissolved N pool during January and April but only 2-6% during August. Dissolved organic N (DON) concentrations increased between January and August though the carbon (C) : N (mol : mol) of the DON pool declined. Of the substrates tested, amino acids supported the bulk of both N and C nutrition in both size fractions during January and April (ice-covered). Urea generally had the lowest uptake rate under ice-covered conditions; uptake of urea-C was only detectable in August. Though previous Arctic studies focused largely on nitrate, we found nitrate uptake was generally lower than other substrates tested. The sharp decline in nitrate concentration between April and August, however, indicates a drawdown of nitrate during that period. Rates of ammonium uptake were highest in August, when it was the dominant N substrate used. During all sample periods, rates of ammonium regeneration were sufficient to supply ammonium demand. Rates of nitrification varied between sample periods, however, with much higher rates seen in January and April. [ABSTRACT FROM AUTHOR]

Due to its flexibility, the multiple-indicator, multiple-causes (MIMIC) model has become an increasingly popular method for the detection of differential item functioning (DIF). In this article, we propose the mediated MIMIC model method to uncover the underlying mechanism of DIF. This method extends the usual MIMIC model by including one variable or multiple variables that may completely or partially mediate the DIF effect. If complete mediation effect is found, the DIF effect is fully accounted for. Through our simulation study, we find that the mediated MIMIC model is very successful in detecting the mediation effect that completely or partially accounts for DIF, while keeping the Type I error rate well controlled for both balanced and unbalanced sample sizes between focal and reference groups. Because it is successful in detecting such mediation effects, the mediated MIMIC model may help explain DIF and give guidance in the revision of a DIF item. [ABSTRACT FROM AUTHOR]

The Arctic is warming at a rate nearly twice the global average, leading to thawing permafrost, increased coastal erosion, and enhanced delivery of riverine terrestrially-derived dissolved organic matter (tDOM) to coastal waters. This humic-rich tDOM has the ability to attenuate light required for photosynthesis and stimulate heterotrophic growth by supplying a source of labile organic carbon. Due to tDOM's high carbon to nitrogen (C : N) ratio, additional nitrogen is required for microorganisms to utilize this excess carbon for growth, thus exacerbating competition between autotrophs and heterotrophs for limiting nutrients and potentially reducing primary production. The effect of Arctic tDOM additions on nitrate uptake by two microplankton size fractions in the coastal Chukchi Sea was quantified using 15N tracer methods. To assess the biogeochemical vs. spectral impacts of tDOM, the uptake incubations were amended with either tDOM or light attenuating films that mimic light absorption by the tDOM. Nitrate uptake and primary production rates in the larger, predominantly phytoplankton, size fraction generally decreased with increasing tDOM additions. The change in light attenuation alone accounted for a ∼ 50% reduction in nitrate uptake. Responses in the smaller size fraction varied seasonally with tDOM additions stimulating uptake in spring and suppressing it in summer. The largest variation in summer nitrate uptake can be explained by the shared effect of biogeochemistry and light attenuation. Therefore, large increases in tDOM delivery currently occurring and predicted to increase in the coastal Arctic, could reduce primary production, broadly impact nitrogen and carbon cycling, and affect higher trophic levels. [ABSTRACT FROM AUTHOR]

Background: We determined the prevalence of urethral Mycoplasma genitalium (MG) infection and whether infection was associated with circumcision status among men enrolled in the randomized trial of medical male circumcision to prevent HIV acquisition in Kisumu, Kenya.Methods: MG and Trichomonas vaginalis were detected in first void urine by APTIMA transcription-mediated amplification assay. first void urine and urethral swabs were assessed for Neisseria gonorrhoeae (NG) and Chlamydia trachomatis (CT) by polymerase chain reaction assay. Herpes simplex virus type 2 antibodies were detected by IgG ELISA. Multivariable logistic regression identified factors associated with MG infection.Results: Specimens were collected between July and September 2010, and 52 (9.9%; 95% confidence interval [CI]: 7.3%-12.4%) MG infections were detected among 526 men. N. gonorrhoeae and T. vaginalis were not associated with MG. CT coinfection was 5.8% in MG-infected men, and 0.8% among MG-uninfected men (P = 0.02). MG infection was predominantly asymptomatic (98%). The prevalence of MG was 13.4% in uncircumcised men versus 8.2% in circumcised men (P = 0.06). Being circumcised nearly halved the odds of MG (adjusted odds ratio [aQR] = 0.54; 95% CI: 0.29-0.99), adjusted for other variables significant at the P < 0.05 level: herpes simplex virus type 2 infection (aOR = 2.05; 95% CI: 1.05-4.00), CT infection (aOR = 2.69; 95% CI: 1.44-5.02), and washing the penis ≤1 hour after sex (aOR = 0.47; 95% CI: 0.24-0.95).Conclusions: MG infection was reduced among men who were circumcised, adding to the benefits of male circumcision in preventing several sexually transmitted infections. [ABSTRACT FROM AUTHOR]

Patients with Parkinson's disease experience motor and perceptual timing difficulties, which are ameliorated by dopaminergic medication. We investigated the neural correlates of motor timing in Parkinson's disease, including the effects of dopaminergic medication on patterns of brain activation. Eight patients with Parkinson's disease and eight healthy controls were scanned with H(15)(2)O positron emission tomography while engaged in three tasks: synchronization (right index finger tapping in synchrony with a tone presented at 1 Hz), continuation (tapping at 1 Hz in the absence of a tone), and a control simple reaction time task. During the first 6 scans, the patients were assessed after overnight withdrawal of medication. Scans 7-12 were completed with the patients in the 'ON' state, after injections of apomorphine, a dopamine receptor agonist. For the healthy controls, relative to the control reaction time task, motor timing (synchronization + continuation) was associated with significantly greater activation in left medial prefrontal cortex (Brodmann area 10, 32), right hippocampus, bilateral angular gyrus (Brodmann area 39), left posterior cingulate (Brodmann area 31) and left nucleus accumbens/caudate. This pattern of brain activation during motor timing was not observed for patients, who showed significantly greater activation in bilateral cerebellum, right thalamus and left midbrain/substantia nigra compared to the control participants. Relative to the externally-paced synchronization task, the internally controlled continuation task was associated with greater activation in the dorsolateral prefrontal cortex (Brodmann area 46/9) in both the control and Parkinson's disease groups. Analysis of medication-related effects indicated that cortical activation was significantly more predominant during motor timing when the patients were 'ON' medication, whereas pallidal and cerebellar activations were evident 'OFF' medication. Effective connectivity analysis established that activity in the left caudate nucleus was associated with increased activity in the right lentiform nucleus and cerebellum 'OFF' medication, and with increased activity in the prefrontal cortex 'ON' medication. These results suggest that in Parkinson's disease, in the 'OFF' medication state, excessive inhibitory pallidal outflow is associated with a lack of adequate frontal activation and reliance on the cerebellum for motor timing. In contrast, our results establish for the first time that administration of dopaminergic medication increases striatal-frontal connectivity between the caudate nucleus and prefrontal cortex during motor timing. [ABSTRACT FROM AUTHOR]